A mass spectrum analysis method is an analysis method for ionizing material particles (atoms or molecules) into ions, arranging them according to spatial position, time sequence or the like by a suitable stable or changeable electrical field or magnetic field to obtain a charge-to-mass ratio separation, and detecting their intensity for quantitative and qualitative analysis. As the mass spectrum analysis method detects the material particles directly and has characteristics of high sensitivity, high resolution, high flux and high applicability, the mass spectrometer and the mass spectrometric technique is significant in the modern science and technology. With the development of sciences, such as life science, environment science and medical science, and due to the requirements of food security, national security and international anti-terrorism, the mass spectrometer has been one of analyzers in the fastest-growing demand. Especially, when the chromatography-mass spectrometry linked technique and relevant instruments appear, they become very popular and even indispensable in the above fields since they have high separation function and high detection sensitivity to a complex matrix.
A mass analyzer is a component of mass spectrometer and used for separation of ions according to the mass to charge ratio. An ion trap is an important mass analyzer and has a principle of first storing ions in a trap and then separating the ions for detection. As compared with a mass analyzer without an ion trap, a mass analyzer with an ion trap can store ions, so an MSn operation (mass spectrometric operation) can be performed in the mass analyzer with an ion trap.
An ion trap has various structure like a traditional 3D ion trap, a linear ion trap made by an American company and a rectangular ion trap invented by a doctor in US, wherein the rectangular ion trap can overcome problems about small capacity of ion storage in the traditional 3D ion trap, high process complexity for the linear ion trap and so on.
An operation mode of an ion trap can be divided into two phases: an ion injection storage phase and an ion separation detection phase. In the ion injection storage phase, it requires ions as much as possible within a unit time, thereby obtaining an ion detection signal with high intensity.
An operation mode of a rectangular ion trap in the ion injection storage phase is provided as follows: an ion (with positive charge, for example) having a certain speed enters the ion trap via a central hole or gap of a front end cover (in this stage, the front end cover is negatively charged to attract the ion with positive charge, so that the ion with positive charge enters the ion trap), and moves at a high speed under the effect of a radio frequency electrical field;
when the ion with positive charge moves close to a rear end cover, the rear end cover (in this stage the rear end cover is positively charged) repels the ion with positive charge to a center of the ion trap; when the ion with positive charge moves from the center of the ion trap to the front end cover, due to the attraction of the front end cover, the ion with positive charge is generally drawn out of the ion trap and impacted on an electrode sheet when it enters the ion trap once again, so buffer gas is generally injected into the ion trap and used to impact the ion with positive charge so as to reduce the kinetic energy of the ion with positive charge; accordingly, it can reduce the possibility of the ion with positive charge entering the ion trap and then drawn out.
However, when the buffer gas is less, it is not enough to reduce the kinetic energy of the ion with positive charge, and hence the number of ions with positive charge out of the ion trap is largely increased; but if the buffer gas is too much, although it can store more ions with positive charge within a unit time, it destroys the basic requirement of the detection system on the vacuum degree and affects the operation of the ion separation detection in the next phase. Accordingly, it generally injects a balanced flow rate of buffer gas to balance both the ion injection and the ion detection, but either the ion injection or the ion detection is hard to reach to a high property.
According to experiments and simulations, it shows that the rectangular ion trap in the prior art has a phenomenon that an ion enters the ion trap and then gets out of the ion trap in the ion injection storage phase. The phenomenon reduces the number of ions in storage within a unit time and affects detection effect, particularly the detection on a low abundance of ions, but a characteristic component in a complex sample is generally an ion in a low abundance. At present, the detection on a characteristic component in a complex sample tends to accurately detect the characteristic component in the complex sample quantitatively and qualitatively.
In U.S. Pat. No. 6,838,666, a new geometry ion trap and its use as a mass spectrometer is described. The ion traps can be combined linearly and in parallel to form systems for mass storage, analysis, fragmentation, separation, etc. of ions. The ion trap has a simple rectilinear geometry with a high trapping capacity. It can be operated to provide mass analysis in the mass-selective instability mode as well as the mass-selective stability mode. Arrays of multiple ion traps allow combinations of multiple gas-phase processes to be applied to the trapped ions to achieve high sensitivity, high selectivity and/or higher throughput in the process of ion analysis.